I hear the Center controllers on all of those feeds. I run the GDM/CON feed personally and know that Center is always audible, with one exception: on 134.7 there are two transmitters, one in Gardner, MA (audible) and one in Lebanon, NH (not audible, too far). The controller on the CON sector can choose between those two transmitters. So that is the only case that I know of on those listed feeds where the controller might be inaudible.
Dave